Exhaust gas recirculation valve

ABSTRACT

A control valve assembly, including a single diaphragm therein, is responsive to the complementary and superimposed effects of the subatmospheric pressure created at an induction passage slot traversed by the edge of the throttle and to the superatmospheric pressure occurring in the exhaust passage, and controls recirculation of exhaust gases from the intake manifold exhaust crossover passage to the intake manifold induction passages.

Unlted States Patent 11 1 1111 3,927,650

Smith et al. Dec. 23, 1975 EXHAUST GAS RECIRCULATION VALVE 3.730.156 5/1973 Sarto 123/119 A I 3.762.384 l0/l973 Day at al. [23/119 A [75] Inventors. Claude A. Snuth Sandusky' David 3 834 366 9 1974 K b I23 119 A E. Taylor, Huron; Donald L. I mgs my W'll' P rt 1' ll I mm o C Into of Ohm Primary Examiner-Wendell E. Burns i l Assign: Minors Corporation, Assistant Examiner-David D. Reynolds 'QP Mlch- Attorney, Agent, or Firm-C. K. Veenstra [22] Filed: Nov. 28, 1973 [211 App]. No.: 419,667 1 1 ABSTRAC A control valve assembly, including a single dia- 52 us. (:1 123/119 A Phragm therein, is resPonsive mPlememarY [51] Int. Cl. F02M 25/06 and Superimposed effects of the subatmospheric Pres' 5 Field f Search I23 19 251/61 61 sure created at an induction passage slot traversed by 5 1 the edge of the throttle and to the superatmospheric pressure occurring in the exhaust passage, and con- [5 References Cited trols recirculation of exhaust gases from the intake UNITED STATES PATENTS manifold exhaust crossover passage to the intake manifold induction passages. 3.231615 3/1966 Daigh t l23/ll9A 1 3,507,260 4/1970 Walker 123/119 A 2 Claims, 4 Drawing Figures US. Patent Dec.23, 1975 Sheet10f2 3,927,650

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2206 E3393 BEE ammoammanw EXHAUST GAS RECIRCULATION VALVE BACKGROUND OF THE INVENTION This invention relates to a novel valve means designed to control recirculation of exhaust gases.

The function of an exhaust gas recirculation valve is to admit a portion of combustion products exhausted from the engine into the intake manifold to dilute the fuel-air intake charge normally aspirated into the cylinders. The dilution or so-called recirculation effect impedes the combustion reaction and accordingly is believed to reduce peak combustion pressures and temperatures, thereby lessening the amount of oxides of nitrogen formed during the combustion process. (I-Ienceforth, oxides of nitrogen will be referred to as NO, for brevity.)

A variety of methods have been investigated for the purpose of reducing NO, formation. These include such methods as retarding the spark and providing exhaust leak holes into the intake manifold, as well as including more advanced systems based on complex metering valves to recirculate the exhaust gas in response to various engine operating parameters. It has been determined by testing that effective reduction of NO, is achieved when a portion of the exhaust proportional to the engine mass air flow is recirculated. For this reason, recirculating valves operatively connected to and positioned by pressure responsive servomotors have found common usage in automotive applications.

One of the more prevalent varieties of the aforementioned recirculation valves is that responsive to a vacuum signal originating from the carburetor throttle region, as set forth in US. Pat. No. 3,641,989, wherein it is disclosed that exhaust gases are recirculated through the induction system under the control of a valve assembly responsive to the vacuum signal created at an induction passage slot traversed by the throttle, a so-called ported vacuum system. In that system, the vacuum signal increases as the throttle traverses the slot during throttle opening movement, and the vacuum responsive servomotor accordingly opens the control valve to increase the recirculation of exhaust gases to the induction system.

Another proposed variety of the aforesaid recirculation valves includes valve-controlling servomotors signaled by the superatmospheric pressure occurring in the exhaust passage, henceforth termed exhaust back pressure recirculation valves.

in this type of valve, the exhaust back pressure signal increases with increasing exhaust flow, thereby directing the servomotor controlling the valve to increase the amount of recirculated exhaust gas because of the increased engine air flow attendant with the increased back pressures.

Returning now to a discussion of the aforedescribed signals, it should first be pointed out that a pressure (or vacuum) signal with an amplitude proportional to engine air flow is highly desirable for recirculation valve actuation and control. However, the carburetor ported vacuum signal has a parabolic air flow versus signal amplitude curve, which maximizes in the middle of the normal range of the engine air flow. While the ported vacuum signal is useful at low engine air flow for controlling a servomotor to modulate an exhaust recirculation valve, the signal amplitude is too small to be useful at high engine air flows which accompany rapid accelerations or wide open throttle operation. Under these conditions, a valve controlled in this manner would be less than effective for providing an increased amount of exhaust gas recirculation to the induction passages.

Alternately, the amplitude of the back pressure signal obtained from the exhaust passage increases steadily with increasing exhaust or engine air flow. Although this signal is small at low air flows, its amplitude is larger than the ported vacuum signal at higher exhaust flows and heavy accelerations. It is, therefore, highly 0 desirable that some means for combining or superimposing the aforesaid signals be developed to actuate the recirculation valve in response to engine air flow.

servomotors for controlling the recirculation valves generally comprise a chamber or a pair of chambers formed in a hermetically sealed housing partitioned by a resilient diaphragm defining the chambers. A pressure differential acting across the diaphragm causes a rod secured to the diaphragm to slide through a bushing in the housing, thereby positioning a metering valve or plug in accordance with the diaphragm deflection. The construction of the chambers allows each distinct chamber to be exposed to a pressure signal arising in the induction passage, atmosphere, or elsewhere in the engine. In some cases, a plurality of diaphragms have been included in the housing to define a plurality of chambers, thereby making the servomotor responsive to more than one pressure signal.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an improved valve assembly for controlling the amount of gas recirculated to the engine which differs from the prior art in the following respects, among others:

1. Actuation of the servomotor and positioning of the valve is accomplished by the use of complementary effects to the exhaust back pressure and ported vacuum signals acting on opposite sides of a resilient diaphragm. Although they complement each other, the signals are combined or superimposed in a novel manner to provide a valve position or lift proportional to engine air flow throughout the normal engine operating range, and are accordingly capable of actuating a valve to provide exhaust recirculation proportional to engine air flow. It should be noted that the use of the term superimposed should not imply the communication or mixing of pressure signals, which would not achieve the desired response if both pressure signals were admitted to one chamber adjacent the diaphragm, but rather to the complementary and superimposed effects of the two distinct pressure signals acting on a pressure responsive means. In the preferred embodiment, the pressure responsive means consists of a single convoluted diaphragm, and said pressure signals act on opposite sides of the diaphragm.

2. The present invention minimizes the potential for the valve failing to operate due to build-up of combustion deposits by reducing the number of slidingly engaging members in the design, as well as by providing a spherical seat and conical valve to improve and ensure closure of the valve.

By virtue of these distinguishing features, the following benefits are accordingly obtained:

1. An improved exhaust recirculation valve assembly uses the complementary and superimposed ported vacuum and exhaust back pressure signals to actuate the valve, resulting in an improved recirculation technique for recirculating exhaust gas to the induction passage in proportion to engine air flow;

2. Improvements in component durability and repeatability of the valve functional characteristics are realized due to the extensive use of corrosion-resistant metals and the minimization of the number of slidingly engaging components; and

3. By providing the servomotor and the valve in a single housing, fabrication cost economies may be realized.

The details and other objects and advantages of this invention are set forth in the remainder of the specification and are shown in the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view ofa V-8 engine intake manifold containing induction passages and an exhaust crossover passage, together with a carburetor spacer plate containing an exhaust gas recirculation control valve assembly;

FIG. 2 is a schematic sectional view of the FIG. 1 manifold and spacer plate showing induction passage plenums and the exhaust crossover passage in the manifold and the exhaust gas recirculation passage in the spacer plate, together with the carburetor throttle body, and showing the exhaust gas recirculation control valve assembly in an enlarged view;

FIG. 3 is a detailed enlargement of the exhaust gas recirculation control valve assembly with a section taken in the center of the assembly as shown in FIG. 1 to illustrate the valve construction; and

FIG. 4 is a graph of the various aforedescribed signal amplitudes carburetor ported vacuum, exhaust back pressure, and superimposed versus engine air flow.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an intake manifold has a pair of vertical primary riser bores 12 and 14 and a pair of larger vertical secondary riser bores 16 and 18. Riser bores 12 and 16 open to an upper horizontal plenum 20 connected forwardly (leftwardly as viewed in FIG. I) to a pair of transverse runners 22 and 24 and connected rearwardly (rightly as viewed in FIG. I) to another pair of transverse runners 26 and 28. Similarly, riser bores 14 and 18 open to a lower horizontal plenum 30 connected forwardly to a pair of transverse runners 32 and 34 and rearwardly to another pair of transverse runners 36 and 38.

An exhaust crossover passage 40 extends transversely to the left hand side of manifold 10 beneath plenums 20 and 30 and receives a portion of the exhaust gases discharged from the engine combustion chambers (not shown).

An insert plate 42 is secured on manifold 10 and has primary riser bores 44 and 46 and secondary riser bores 48 and 50 which meet riser bores l2, 14, 16 and 18 of manifold 10.

Referring to FIG. 2, a carburetor 52 is secured on insert plate 42 and has primary throttle bores 54 and 56 which meet, respectively, primary riser bores 44 and 46 of insert plate 42. Carburetor 52 also has secondary throttle bores (not shown) which meet secondary riser bores 48 and 50 of insert plate 42.

A bore 58 in manifold 10 leads upwardly from exhaust crossover passage 40 to the first or upstream portion 60 of an exhaust recirculation passage formed in insert plate 42. The upstream portion 60 leads through an annular well 62 formed in insert plate 42 to a second or downstream portion 64 of the exhaust recirculation passage. A control valve assembly 66 is disposed in well 62 intermediate upstream portion 60 and downstream portion 64 to control the amount of recirculation permitted therethrough, as will be explained in further detail. It should be noted that downstream portion 64 of the exhaust recirculation passage divides into a pair of branches 68 and 70 which lead to the primary riser bores 44 and 46 in insert plate 42.

It should be appreciated that both portions 60 and 64 of the exhaust recirculation passage may be integrated in manifold 10 rather than in separate insert plate 42.

Referring to FIG. 3, a detailed description of the preferred embodiment of the control valve assembly will now be presented Control valve 66 includes a base member 72 residing in annular well 62 of the insert plate 42. In the preferred embodiment, base member 72 is fabricated from stainless steel, for example in a conventional pressing/punching process, to have a radially extending upper flange portion 74, a lower recess portion 76, and a rounded, upwardly convex seat 78 surrounding a valve orifice 80. A plurality of circularly disposed holes 82 extending through base member 72 are punched or formed in a conventional manner for purposes to be described subsequently.

It should be noted that base member 72 of the valve assembly sealingly engages insert plate 42 by means of gaskets 84 and 86, which engage upper flange portion 74 and lower recess 76 of the base member 72, respectively, to provide sealing engagement between the aforementioned portions of base member 72 and the insert plate 42 to prevent the leakage of exhaust gas therearound.

A blast shield 88, which prevents direct exhaust gas impingement on diaphragm 98, is formed in a preferred embodiment of the present invention from corrosionresistant stainless steel and has an annular ear 92 which resides on a land of base member 72. Blast shield 88 has a center hole 94 for allowing a valve subassembly 96 to be coaxially disposed in a noncontacting manner therethrough.

A third major component of control valve 66 is a diaphragm 98, made in a preferred embodiment from a resilient, corrosion-resistant material such as a precipitation hardened stainless steel. An upwardly extending annular car 100 of diaphragm 98 conforms to and resides within the annular ear 92 of blast shield 88. A plurality of circular convolutions 102 disposed at regular radial intervals from the central axis of the valve subassembly 96 are provided to allow the diaphragm to experience nondestructive flexure and bending under the influence of different pressures acting on opposite sides of the diaphragm. A center hole 104 located in diaphragm 96 is provided so that the diaphragm can be secured to the valve subassembly 96 in a manner to be described.

A fourth component of the control valve 66 is a resilient spring member 106 which opposes the inherent downward biasing or closing force of diaphragm 98. This inherent downward biasing is due in part to convolutions 102. Also, the placement and position of the diaphragm is such that the equilibrium position of the diaphragm is below that shown in FIG. 3. To offset this closing force, spring 106 is included to buck the diaphragm by providing a passive yet constant preload in the upward or valve opening direction. It should be noted that this preload is insufficient to open the valve without the assistance of the opposing gaseous forces, to be described, and vice-versa.

Spring 106 has an upper disposed center hole 108 in a center portion 109 for allowing the valve subassembly 96 to be disposed coaxially therethrough, and an outwardly extending waveform rim 110 for retaining the spring in the position shown in FIG. 3. Also, spring 106 has, in the preferred embodiment, a plurality of ribs 111 connecting center portion 109 and rim 110 so that gas may freely pass through the spring. A spring retainer 112, having an annular ear I14 and an outer annular ear 116 conforming to and residing within annular ear 92 of the blast shield 88, is provided to constrain spring 106 in the position shown. Lower flange 110 of the spring abuts, but is not secured to inner annular ear 1 14 of spring retainer 1 12, so that the spring may freely rise vertically in the downwardly extending well 115 of the retainer 112. lt is important to note that this construction precludes the biasing of the valve subassembly 96 in a seating direction by spring 106.

A thin metal cover member 118 having a raised portion 120, a flat portion 122, and a sealing flange 124 abuts a flat portion 126 of spring retainer 112 and the upper flange 74 of base member 72 in a manner which hermetically seals control valve assembly 66 by means of an inwardly turned rim or crimp 127 of cover member 118.

The valve assembly and heretofore described elements are abutted in a manner which secures diaphragm 98, spring retainer 112, and blast shield 88 to the two halves of the valve housing upper cover member 118 and lower member 72. Specifically, flat portion 124 of cover member 1 18 abuts the flat portion 126 of the spring retainer, thereby forcing the retainer, diaphragm, and blast shield into engagement by means of the aforesaid, conforming annular ears 116, 100, and 92. Annular ear 92 resides within and is thus engaged by land 90 of base member 72, so that the abovedescribed engagement maintains base member 72 in engagement with blast shield 88, diaphragm 98, spring retainer 112, and cover member 118. Crimp 127 of cover member 118 over upper flange 74 of base member 72 further provides and ensures engagement for all of the abovedescribed components and also seals the valve interior from the atmosphere.

Flange 74 of base member 72, gasket 84, and flange 124 of cover member 118 are provided with a plurality of holes 128. Standard fasteners such as bolts 130 may extend through the former to threadably engage tapped holes 132 of insert plate 42 in a conventional manner to sealingly secure the control valve assembly to insert plate 42 in annular well 62. In this manner, gaskets 84 and 86, which may consist of resilient heat resistant gasket material such as asbestos, may be compressed by the force imparted by bolts 130 on sealing flange 74 and recess 76 of the base member to provide a gas-tight seal between the control valve assembly 66, the exhaust passages, and the atmosphere.

By observing the complete control valve assembly, components of which have been heretofore described, it may be noted that two distinct chambers are formed, one above and one below diaphragm 98. An upper chamber 134 includes that region defined above diaphragm 98 and below cover member 118, as there is no gas-tight seal occurring between the spring and spring retainer 112 due to the ribs 111 and the cavities therebetween. Upper chamber 134 is exposed to a carburetor vacuum signal by a vacuum fitting 136 formed in the top of cover member 118 and connected to a hose 138 extending to the carburetor. The manner and means by which the carburetor vacuum signal is generated will be described subsequently.

A lower chamber 140 includes that region occurring above base member 72 and below diaphragm 98. The pressure occurring above blast shield 88 is equal to that occurring below blast shield 88 because of a leak path defined through hole 94 of the blast shield.

it may be noted that exhaust gas is swirled in annular well 62 before it is admitted through holes 82 in base member 72 to the lower chamber. This swirling action dampens the pulsations inherent in the exhaust passages as a result of the multiple, cyclical exhaust strokes of a multicylinder engine. Lower chamber 140 and annular well 62 also provide a reservoir which further dampens or reduces the exhaust pressure pulsations occurring on the underside of diaphragm 98, thereby reducing the amplitude of cycle-to-cycle excursions experienced by the diaphragm and the valve subassembly.

The valve subassembly 96, disposed along the central axis of control valve assembly 66, consists of two components in the preferred embodiment of FIG. 3. A lower portion 142 has a lower rim 144 centrally disposed in downstream portion 64 of the exhaust recirculation passage, an intermediate flange 146 providing a valve member having a conical valve surface 148 formed thereon, a central cylindrical shank 150, a counterbore 152 coaxial with the central axis of valve assembly 66, and an upper rim 154. A countersunk recess 156 is provided in the bottom of bore 152 to accept a flare on the lower end 158 of an upper portion or central pin 160. In addition, central pin 160 has a similar flared upper end 162 which resides in a countersink 163 of a washer 164.

It may be noted that central pin 160 protrudes through center hole 108 of spring 106 to secure the spring to the central pin. Furthermore, central pin 160 has a mid-disposed lip 166 which in the preferred embodiment, abuts the material surrounding center hole 104 of diaphragm 98 thereby snagging the center of diaphragm 98 against the rim 154 of lower portion 142 of the valve subassembly 96. In this manner, valve subassembly 96, diaphragm 98 and spring 106 are operatively connected in a manner which minimizes sliding friction therebetween.

Minimization of the number of slidingly engaging parts is further accomplished by disposition of valve subassembly 96 through center hole 94 of blast shield 88 in a non-contacting construction. A bushing 168, having an H-section as shown in FIG. 3, is slidingly disposed and laterally free in center hole 94 of blast shield 88 so as to provide a floating fit for shank of valve subassembly 96. Bushing I68 restricts the flow of exhaust particulants and/or contaminants into the region between blast shield 88 and diaphragm 98, but allows the underside of diaphragm 98 to be exposed to the exhaust back pressure occurring below blast shield 88 and to position the response of the diaphragm thereby.

It should be noted that central pin may be secured to lower portion 142 of the valve subassembly 96 externally of the control valve assembly prior to the installation of the cover member 118. in addition, conventional fastening means, such as a bolt or a separate rivet (not shown), extending through a bore in the central pin may be used in place of flared portions 158 and 162 to secure the central pin to the lower portion in the aforedescribed manner. Also, the use of a bolt would allow a certain amount of preadjustment of the tension of the spring 106 which bucks the downward urging of diaphragm 98 to allow calibration of the amount of force engaging valve surface 148 of the valve subassembly 96 against seat 78 of base member 72 the bolt could be tightened to vary the preload of the spring on the diaphragm.

Returning now to the description of the carburetor, the hose 138 extends from vacuum fitting 136 to a vacuum fitting 170 communicating with a slot or port 172 disposed in throttle bore 56. Carburetor throttles 174 and 176 are rotatably disposed in primary bores 54 and 56 respectively for controlling air flow to the engine. A slot or port 172 is disposed adjacent and extends above and slightly below the upstream edge of throttle 174 so as to subject hose 138 and thereby chamber 134 to the vacuum signal created at slot 172.

In operation, an air-fuel mixture, or air alone in the case of the fuel injected engine, is drawn into the induction passage difined by carburetor throttle bores 54 and 56, insert plate riser bores 44, 46, 48, 50 and manifold riser bores 12, 14, 16, and 18; manifold plenum 20 and and manifold runners 22, 24, 26, 28, 32, 34, 36, and 38. When throttle bore 56 above throttle 174 bleeds air into the upper portion of slot 172 and increases the manifold pressure sensed by the lower portion of slot 172, as would occur when throttle 174 is closed, the resultant pressure is communicated through holes 138 to chamber 134 above diaphragm 98, so that upper chamber 134 is exposed to substantially atmospheric pressure. The exhaust back pressure occurring in lower chamber 140 below diaphragm 98 when throttles 174 and 176 are closed will be substantially the same as that occurring in chamber 134 above diaphragm 176. This arises because at closed throttle, air flow to the engine is reduced and exhaust back pressure approaches atmospheric due to the low exhaust flow occurring in the exhaust passages. Accordingly, the superimposition of gaseous forces thus occurring on diaphragm 98 is insufficient to raise diaphragm 98 against its inherent downward bias. Valve subassembly 96 is thereby maintained in sealing engagement with the valve seat 78 to prevent recirculation of the exhaust gases through control valve lower chamber 140 and downstream portion 64 of exhaust recirculation passage.

As throttles 174 and 176 are opened to a part throttle position, the upstream edge of throttle 174 traverses slot 172 and a greater portion of slot 172 is subjected to the subatmospheric manifold pressure below throttle 174 while a lesser portion of slo 172 is subjected to substantially atmospheric pressure above throttle 174. This results in a lower pressure signal which is communicated through hose 138 to upper chamber 134 of valve assembly 66. Simultaneously, increased air flow as a result of the opening of throttles 174 and 176 increases the exhaust flow through the exhaust passages. Accordingly, this increases the exhaust back pressure occurring in lower chamber 140. The superimposition of gaseous forces thus occurring on diaphragm 98 raises the diaphragm against its downward bias. Accordingly, flange 146 is lifted away from valve seat 78 to allow recirculation of exhaust gases from exhaust crossover passage through bore 58, upstream passage 60, annular well 62, lower chamber 140, downstream passage 64, and branches 68 and 70 to riser bores 44 and 46.

lt should be pointed out that valve assembly 66 also provides recirculation at wide open throttle operation. At such time, the pressure signal from port 172 is equal or near equal to manifold pressure and both approach atmospheric pressure. Simultaneously, the exhaust back pressure at wide open throttle is substantially above atmospheric pressure. Thus, the upward gaseous force acting below diaphragm 98 is sufficient to overcome the downward bias of diaphragm 98, and valve subassembly 96 is further raised from seat 78 to provide increased recirculation.

It will be appreciated, of course, that the size and shape of seat 78 and the conforming lower portion 142 of valve subassembly 96, the resilient characteristics of convoluted diaphragm 98 and ribbed spring 106, and the shape and location of slot 172 all must be considered to achieve recirculation of exhaust gases in the desired manner.

The qualitative nature of the afoementioned pressure/vacuum signal have been alluded to as being complementary. Referring to FIG. 4, a graph of signal amplitude (the magnitude of the signal) versus engine air flow (the independent variable) is presented. It can be seen that the carburetor ported vacuum signal has a parabolic signal amplitude curve with a maximum in the middle range of engine air flow. At higher engine air flow the carburetor signal decreases, thereby becoming of little utility as an indicator of engine air flow at wide open throttle or hard acceleration operating conditions.

The exhaust back pressure has an ever-increasing characteristic as shown in FIG. 4. For most of the lower air flows, the amplitude of the back pressure is small. Only at high air flows is the signal of appreciable amplitude. Therefore, this signal is of inconsequential value as an indicator of engine air flow at low to moderate air flows.

Finally, the resulting and superimposed valve actuating signal" that the present invention achieves is shown to complement the deficiencies of the aforesaid signals by providing a signal" more nearly proportional to engine air flow than heretofore achieved.

What is claimed is:

1. An exhaust gas recirculation control valve assembly for an internal combustion engine having an induction passage for air flow to the engine, a throttle rotatably disposed in said induction passage for controlling air flow therethrough, a slot in said induction passage disposed adjacent and traversed by said throttle, an exhaust passage for exhaust gas flow from the engine, and a recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a housing adapted for disposition in said recirculation passage, said housing having an inlet aperture for receiving exhaust gases from said first recirculation passage portion and an outlet orifice for discharging exhaust gases to said second recirculation passage portion, a valve seat formed in said housing about said orifice, a valve member associated with said valve seat for controlling the amount of exhaust gas recirculated, a resilient diaphragm partitioning said housing and secured to said said valve member and providing means for urging said valve member against said valve seat, one side of said diaphragm being exposed to an exhaust back pressure signal occurring in said housing upstream of said valve seat and tending to move said valve member away from said valve seat upon an increase in said signal, said housing defining a chamber on the other side of said diaphragm, and means for subjecting said chamber to the pressure signal created at said slot to cause said diaphragm to tend to move said valve member away from said valve seat upon a decrease in said slot pressure signal, whereby said valve member is moved away from said valve seat against the urging of said diaphragm by the complementary and superimposed effects of said pressure signals acting on said diaphragm to control the amount of exhaust gas recirculated through said recirculation passage to said induction passage.

2. For an internal combustion engine having an induction passage for air flow to the engine, a throttle rotatably disposed in said induction passage for controlling air fiow therethrough, a slot in said induction passage disposed adjacent and traversed by said throttle, an exhaust passage for exhaust gas flow from the engine, and a recirculation passage connecting said exhaust passage and said induction passage posterior and throttle, said recirculation passage having an upstream portion and a downstream portion; an exhaust gas recirculation valve assembly comprising:

a. a base member adapted for registration with said recirculation passage between said upstream portion and said downstream portion, said base member having an upper flange portion radially extending therefrom, a lower recess portion formed in the bottom of said base member, a valve orifice formed in the center of said base member, an upwardly convex seat portion formed in said base member and surrounding said valve orifice, a land portion formed in said base member between said lower recess and said upper flange portion, at least one hole radially extending through said base member for communicating exhaust gases from said upstream portion through said hole and said valve orifice to said downstream portion, said hole disposed between said land portion and said lower recess;

b. a blast shield member having an annular ear portion residing on said land portion of said base member; said blast shield having a center hole formed therein;

c. a resilient diaphragm member having an annular ear portion residing on the lip portion of said blast shield, said diaphragm further having a plurality of circular convolutions disposed at regular radial intervals from the central axis of said valve assembly and further having a center hole formed in said diaphragm;

d. a spring retainer member having an annular ear portion conforming to and residing on said annular ear portion of said diaphragm, said spring retainer having a downwardly extending well portion and an inwardly extending annular ear portion;

e. a spring adapted for registration with said well portion of said spring retainer and having an outwardly extending waveform rim for residing in said well portion, a center portion and a plurality of ribs connecting said rim to said center portion, said spring having a center hole formed in said center portion;

a cover member having a raised portion disposed above said spring and an outwardly extending flat portion, an inwardly turned crimp portion extending from said flat portion of said cover member and around said upper flange portion of said base member for sealingly joining said cover member with said base member, said flat portion of said cover member thereby forcing said spring retainer, said diaphragm, said blast shield and said base member into interengagement, said cover member having at least one hole extending through said flat portion, said base member having at least one hole extending through said upper flange in alignment with said cover member hole, said aligned holes adapted to receive fastening means extending through said cover and base member holes for securing said valve assembly to the engine;

g. a valve subassembly centrally and reciprocably disposed in said valve assembly and having a lower portion and an upper portion, said subassembly portions having a central bore extending therethrough and aligned therebetween, said lower portion having a lower rim portion and a central shank portion, an intermediate flange portion extending radially from said lower portion of said valve subassembly and having a conical valve surface formed thereon and associated with said upwardly convex seat portion of said base member for engagement with said seat portion to close said valve orifice, said upper portion of said valve subassenibly having an intermediate lip portion and an upper flared portion, a washer disposed around said upper flared portion of said valve subassembly, a pin extending through said central bore of said lower portion and said upper portion for forcing the former and the latter into abutting interengagement, so that said lower lip portion of said valve subassembly forces said diaphragm against said central shank portion of said valve subassembly for securing the center of the diaphragm to said valve subassembly, said washer disposed above the center of said spring for fastening said spring to said upper portion, whereby said valve subassembly, said spring and said diaphragm are forced by said seat portion of said base member into a position above the equilibrium position of said diaphragm, so that said diaphragm downwardly urges said valve subassembly and said valve surface towards said valve orifice, but said spring may buck said urging by providing a constant preload in the upward or valve opening direction to reduce the force necessary to raise said valve surface and open said valve orifice;

h. a resilient bushing disposed in said center hole of said blast shield and surrounding said central shank portion of said valve subassembly, said bushing having an upper flange overlying said blast shield and a lower portion underlying said blast shield and an intermediate portion interconnecting said flange, said intermediate portion being smaller in diameter than and disposed in said center hole of said blast shield and defining a leak path around said central shank portion through said center hole of said blast shield and also permitting limited radial movement of said bushing in said center hole;

i. said cover member and said diaphragm defining an upper vacuum chamber formed therebetween;

j. said diaphragm and said base member defining a lower chamber formed therebetween for providing an exhaust flow path from said upstream portion of said recirculation passage through said hole in said base member, said lower chamber and said valve orifice to said downstream portion only when said 12 valve surface is raised from said valve orifice; ber, thereby opening said valve orifice upon a k. means for exposing said upper vacuum chamber to decrease in said subatmospheric pressure; and the subatmospherlc pressure occurring at said slot being f th responsive m i exhaust b k in said induction passage;

l. and means associated with said lower chamber for exposing said lower chamber to the superatmospheric exhaust back pressure occurring in said recirculation passage in a manner which seals said lower chamber, said valve assembly and said recirpressure occurring in said exhaust passage for raising said diaphragm, said valve subassembly, and said valve surface from said base member, thereby opening said valve orifice upon an increase in exhaust back pressure; whereby the culation passage from the adjacent atmosphere; In c omplememary of said Prelimres mlsaid whereby aid valve assembly is responsive to the P E are Supenmposed f comfol subatmospheric pressure occurring at said slot laIlOn of exhaust gases to the md lon p ssag for raising said diaphragm, said valve subassemand t0 the engine. bly, and said valve surface from said base mem- 

1. An exhaust gas recirculation control valve assembly for an internal combustion engine having an induction passage for air flow to the engine, a throttle rotatably disposed in said induction passage for controlling air flow therethrough, a slot in said induction passage disposed adjacent and traversed by said throttle, an exhaust passage for exhaust gas flow from the engine, and a recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a housing adapted for disposition in said recirculation passage, said housing having an inlet aperture for receiving exhaust gases frOm said first recirculation passage portion and an outlet orifice for discharging exhaust gases to said second recirculation passage portion, a valve seat formed in said housing about said orifice, a valve member associated with said valve seat for controlling the amount of exhaust gas recirculated, a resilient diaphragm partitioning said housing and secured to said said valve member and providing means for urging said valve member against said valve seat, one side of said diaphragm being exposed to an exhaust back pressure signal occurring in said housing upstream of said valve seat and tending to move said valve member away from said valve seat upon an increase in said signal, said housing defining a chamber on the other side of said diaphragm, and means for subjecting said chamber to the pressure signal created at said slot to cause said diaphragm to tend to move said valve member away from said valve seat upon a decrease in said slot pressure signal, whereby said valve member is moved away from said valve seat against the urging of said diaphragm by the complementary and superimposed effects of said pressure signals acting on said diaphragm to control the amount of exhaust gas recirculated through said recirculation passage to said induction passage.
 2. For an internal combustion engine having an induction passage for air flow to the engine, a throttle rotatably disposed in said induction passage for controlling air flow therethrough, a slot in said induction passage disposed adjacent and traversed by said throttle, an exhaust passage for exhaust gas flow from the engine, and a recirculation passage connecting said exhaust passage and said induction passage posterior and throttle, said recirculation passage having an upstream portion and a downstream portion; an exhaust gas recirculation valve assembly comprising: a. a base member adapted for registration with said recirculation passage between said upstream portion and said downstream portion, said base member having an upper flange portion radially extending therefrom, a lower recess portion formed in the bottom of said base member, a valve orifice formed in the center of said base member, an upwardly convex seat portion formed in said base member and surrounding said valve orifice, a land portion formed in said base member between said lower recess and said upper flange portion, at least one hole radially extending through said base member for communicating exhaust gases from said upstream portion through said hole and said valve orifice to said downstream portion, said hole disposed between said land portion and said lower recess; b. a blast shield member having an annular ear portion residing on said land portion of said base member; said blast shield having a center hole formed therein; c. a resilient diaphragm member having an annular ear portion residing on the lip portion of said blast shield, said diaphragm further having a plurality of circular convolutions disposed at regular radial intervals from the central axis of said valve assembly and further having a center hole formed in said diaphragm; d. a spring retainer member having an annular ear portion conforming to and residing on said annular ear portion of said diaphragm, said spring retainer having a downwardly extending well portion and an inwardly extending annular ear portion; e. a spring adapted for registration with said well portion of said spring retainer and having an outwardly extending waveform rim for residing in said well portion, a center portion and a plurality of ribs connecting said rim to said center portion, said spring having a center hole formed in said center portion; f. a cover member having a raised portion disposed above said spring and an outwardly extending flat portion, an inwardly turned crimp portion extending from said flat portion of said cover member and around said upper flange portion of said base member for sealingly joining said cover member with said base member, said flat portion of said cover member thereby forcing said spring retainer, said diaphragm, said blast shield and said base member into interengagement, said cover member having at least one hole extending through said flat portion, said base member having at least one hole extending through said upper flange in alignment with said cover member hole, said aligned holes adapted to receive fastening means extending through said cover and base member holes for securing said valve assembly to the engine; g. a valve subassembly centrally and reciprocably disposed in said valve assembly and having a lower portion and an upper portion, said subassembly portions having a central bore extending therethrough and aligned therebetween, said lower portion having a lower rim portion and a central shank portion, an intermediate flange portion extending radially from said lower portion of said valve subassembly and having a conical valve surface formed thereon and associated with said upwardly convex seat portion of said base member for engagement with said seat portion to close said valve orifice, said upper portion of said valve subassembly having an intermediate lip portion and an upper flared portion, a washer disposed around said upper flared portion of said valve subassembly, a pin extending through said central bore of said lower portion and said upper portion for forcing the former and the latter into abutting interengagement, so that said lower lip portion of said valve subassembly forces said diaphragm against said central shank portion of said valve subassembly for securing the center of the diaphragm to said valve subassembly, said washer disposed above the center of said spring for fastening said spring to said upper portion, whereby said valve subassembly, said spring and said diaphragm are forced by said seat portion of said base member into a position above the equilibrium position of said diaphragm, so that said diaphragm downwardly urges said valve subassembly and said valve surface towards said valve orifice, but said spring may buck said urging by providing a constant preload in the upward or valve opening direction to reduce the force necessary to raise said valve surface and open said valve orifice; h. a resilient bushing disposed in said center hole of said blast shield and surrounding said central shank portion of said valve subassembly, said bushing having an upper flange overlying said blast shield and a lower portion underlying said blast shield and an intermediate portion interconnecting said flange, said intermediate portion being smaller in diameter than and disposed in said center hole of said blast shield and defining a leak path around said central shank portion through said center hole of said blast shield and also permitting limited radial movement of said bushing in said center hole; i. said cover member and said diaphragm defining an upper vacuum chamber formed therebetween; j. said diaphragm and said base member defining a lower chamber formed therebetween for providing an exhaust flow path from said upstream portion of said recirculation passage through said hole in said base member, said lower chamber and said valve orifice to said downstream portion only when said valve surface is raised from said valve orifice; k. means for exposing said upper vacuum chamber to the subatmospheric pressure occurring at said slot in said induction passage; l. and means associated with said lower chamber for exposing said lower chamber to the superatmospheric exhaust back pressure occurring in said recirculation passage in a manner which seals said lower chamber, said valve assembly and said recirculation passage from the adjacent atmosphere; whereby aid valve assembly is responsive to the subatmospheric pressure occurring at said slot for raising said diaphragm, said valve subassembly, and said valve surface from said base member, thereby opening said valve orifice upon a decrease in said subatmospheric pressure; and being further responsive to said exhaust back pressure occurring in said exhaust passage for raising said diaphragm, said valve subassembly, and said valve surface from said base member, thereby opening said valve orifice upon an increase in exhaust back pressure; whereby the complementary effect of said pressures on said diaphragm are superimposed to control recirculation of exhaust gases to the induction passage and to the engine. 